Put the word out to people that you know who are fishermen and have them save the fish that are too small - or even the remains, including heads, of the filleted fish. I have a friend that feeds his almost nothing (except occasional vegitation) but the remains of gamefish and he's been keeping his allisnaps in good health for over twenty years now.
Do you live anywhere around a bait shop? How about an Asian market. They carry a lot of different fish and usually at reasonable prices. I go there to buy live blue crabs once in a while. I give them to the snappers as well as crocodilians.